Field of the Invention
The present invention relates to an organic electroluminescent device (or an organic light emitting display device. More particularly, the present invention relates to a flexible organic electroluminescent device capable of minimizing the generation of cracks by a step portion with a line hole formed in a pad region in which cracks are readily generated, or a non-display region including the pad region, and a method for fabricating the same.
Discussion of the Related Art
An organic electroluminescent device, one of flat panel displays (FPDs), has a high degree of luminance and low operational voltage characteristics. Also, because the organic electroluminescent device is a self-luminous device, it has a large contrast ratio, is able to be used as an ultra-thin display, has a response time as fast as a few microseconds (μs) to facilitate implementation of a video, has no limitation in a viewing angle, is stable at low temperatures, and is driven at a low voltage ranging from 5V to 15V of direct current.
Also, the fabrication process of the organic electroluminescent device requires only deposition and encapsulation equipment, which is thus very simple.
The organic electroluminescent device having the foregoing characteristics is divided into a passive matrix type organic electroluminescent device and an active matrix type organic electroluminescent device. In the passive matrix type organic electroluminescent device, scan lines and signal lines cross in a matrix form, and in order to drive each pixel, the scan lines are sequentially driven over time. Thus, in order to obtain the required average luminance, instantaneous luminance corresponding to a value obtained by multiplying the number of lines to average luminance (i.e., instantaneous luminance as high as the product of average luminance and the amount of lines) is required to be obtained.
However, in the active matrix type organic electroluminescent device, a thin film transistor (TFTs) is used as a switching element for turning on or off a pixel region and positioned in each pixel region. The TFT is connected to a power line and an organic light emitting diode (OLED) in each pixel region.
In this case, a first electrode connected to the driving TFT is turned on and off by pixel region, and a second electrode facing the first electrode may serve as a common electrode. The first electrode and the second electrode form the OLED together with an organic light emitting layer interposed therebetween.
In the active matrix type organic electroluminescent device having the foregoing characteristics, a voltage applied to the pixel region is charged in a storage capacitor Cst to supply power until when a next frame signal is applied, whereby the device is continuously driven during a single screen regardless of an amount of scan lines.
Thus, although a low current is applied, the same luminance can be obtained, having advantages in that less power is consumed, a fine pitch can be obtained, and a display size can be increased. These features have led to an increase in active matrix type organic electroluminescent devices being commonly used.
The related art organic electroluminescent device will be described with reference to FIGS. 1 and 2.
FIG. 1 is a plan view illustrating the related art organic electroluminescent display device.
FIG. 2 is a cross-sectional view of the related art organic electroluminescent device taken along line II-Ii in FIG. 1.
In FIG. 1, the related art organic electroluminescent device 10, a display region AA is defined in a substrate (not shown), a non-display region (not shown) having a pad region PD is defined in an outer side of the display region AA, a plurality of pixel regions (not shown) defined as regions captured by the gate lines (not shown) and data lines (not shown) are provided in the display region AA, and power lines (not shown) are provided in parallel to the data lines (not shown).
A TFT is formed in each pixel region (not shown).
In the related art organic electroluminescent device 10, a substrate (11 in FIG. 2) in which the TFT and an organic electroluminescent element (or an OLED) E are formed is encapsulated with a protective film (47 in FIG. 2).
In detail, as illustrated in FIG. 2, the display region AA is defined in the substrate 11, and a non-display region including a pad region PD is defined in an outer side of the display region AA. A plurality of pixel regions (not shown) defined by regions formed by the gate lines (not shown) and the data lines (not shown) are provided in the display region AA, and power lines (not shown) are provided in parallel to the data lines (not shown).
Here, a polyimide layer 15 is formed on the substrate 11 made of a glass material, and a sacrificial layer 13 is formed between the polyimide layer 15 and the substrate 11.
A buffer layer 17 made of an insulating material, e.g., silicon oxide (SiO2) or silicon nitride (SiNx) as an inorganic insulating material, is formed on the polyimide layer 15.
Also, an active layer 19 is formed in each pixel region of the display region AA above the buffer layer (not shown). The active layer 19 includes a channel region 19a made of pure polysilicon and having a central portion forming a channel, and a source region 19b and a drain region 19c formed on both sides of the channel region 19a and having impurities doped with high concentration.
A gate insulating layer 21 is formed on the buffer layer (not shown) including the active layer 19, and a gate electrode 23 is formed to correspond to the channel region 19a of each active layer 19 above the gate insulating layer 21.
Also, a gate line (not shown) is formed to extend from the gate electrode 23 in one direction above the gate insulating layer 21.
An interlayer insulating layer 25 is formed on the entire surface of the display region above the gate electrode 23 and the gate line (not shown). In this case, the interlayer insulating layer 25 and the underlying gate insulating layer 21 include contact holes (not shown) exposing the source region 19a and the drain region 19c positioned on both sides of the channel region 19a of each active layer, respectively.
Also, a data line (not shown) is formed above the interlayer insulating layer 25 including the contact holes (not shown). The data line crosses a gate line (not shown) to define a pixel region, and is made of a metal. A power line (not shown) is formed to be spaced apart from the data line. Here, the power line (not shown) may also be formed to be spaced apart from the gate line and parallel to the gate line (not shown) on the layer in which the gate line (not shown) is formed, namely, on the gate insulating layer.
A source electrode 27a and a drain electrode 27b are formed on the interlayer insulating layer 25. The source electrode 27a and the drain electrode 27b are spaced apart from each other, are in contact with the source region 19b and the drain region 19c, respectively, exposed through the contact holes (not shown), and are made of the same metal as that of the data line (not shown). In this case, the active layer 19, the gate insulating layer 21, the gate electrode 23, and the interlayer insulating layer 25, which are sequentially stacked, and the source electrode 27a and the drain electrode 27b formed to be spaced apart from each other all form a TFT (T).
A first passivation layer 31 having a drain contact hole exposing the drain electrode 27b of the TFT (T) and a planarization layer 33 is formed on the TFT.
Also, a first electrode 35 is formed on the planarization layer 33. The first electrode 35 is in contact with the drain electrode 27b of the TFT (T) through the drain contact hole and is separated by pixel region.
A pixel defining layer 37 is formed on the first electrode 35 to separately form each pixel region. In this case, the pixel defining layer 37 is disposed between adjacent pixel regions.
An organic light emitting layer 39 is formed on the first electrode within each pixel region surrounded by the pixel defining layer 37 and includes light emitting layers (not shown) emitting red, green, and blue light.
Also, a second electrode 41 is formed on substantially the entire surface of the display region AA including on the organic light emitting layer 39 and the pixel defining layer 37. In this case, the first electrode 35, the second electrode 41, and the organic light emitting layer 39 interposed between the two electrodes 35 and 41 form an organic electroluminescent element E.
An organic layer 43 is formed on the entire surface of the substrate including the second electrode 41, and a second passivation layer 45 is formed on the organic layer 43.
A barrier film 47 is positioned on the second passivation layer 45 in order to encapsulate the organic electroluminescent element E and prevent moisture transmission. A press sensitive adhesive (PSA) (not shown) is interposed to be completely and tightly attached to the substrate 11 and the barrier film 47 without an air layer. A polarization plate 53 is disposed on the barrier film 47. In this case, the second passivation layer 45, the PSA, and the barrier film 47 form a face seal structure.
In this manner, the substrate 11 and the barrier film 47 are fixed by the PSA to form a panel state, constructing the related art organic electroluminescent device.
In order to make the organic electroluminescent device 10 configured as described above into a flexible organic electroluminescent device, first, a rear surface of the substrate 11 of the organic electroluminescent device 10 is cleaned, and laser is irradiated to separate the sacrificial layer 13 interposed between the substrate 11 and the polyimide layer 15, thus delaminating the substrate 11 from the organic electroluminescent device 10.
Thereafter, a back plate is laminated on a surface of the polyimide layer 15 of the separated organic electroluminescent device to form a flexible organic electroluminescent device.
However, when the substrate 11 is separated from the organic electroluminescent device to fabricate the flexible organic electroluminescent device, the organic electroluminescent device 10 is bent due to self-stress of the barrier film 47, the polarization plate 53, and the TFT (T) constituting the organic electroluminescent device.
FIG. 3 is a schematic perspective view of the related art organic electroluminescent device illustrating a scenario in which cracks are spread from the pad region of the organic electroluminescent device to cause a curling phenomenon in the organic electroluminescent device.
As illustrated in FIG. 3, during the process of laminating a back plate (not shown) on the surface of the polyimide layer 15 without the substrate 11, bending and spreading are repeated to generate cracks C in a vulnerable region, e.g., the pad region PD to which a flexible printed circuit board (FPCB) is connected, and the cracks C spread even to the TFT part to result in a defective organic electroluminescent device. In particular, after the substrate 11 is removed, the layers constituting the pad region PD are mostly inorganic layers, and the polyimide layer 15 is so brittle as to be vulnerable to a generation of cracks. Thus, in fabricating the related art flexible organic electroluminescent device, because cracks C are generated in the pad region PD to which the FPCB is connected, i.e., a weak region, due to the repetition of bending and spreading to the TFT within the device, to produce a defective organic electroluminescent device.
Also, the cracks increase during a follow-up process to interfere with a signal line of a panel, which leads to defective driving and a defective screen.